Cause

If you have already set up port sharing for a particular TCP or UDP port, or the IP protocol ESP or GRE, then the FRITZ!Box prevents you from creating a second sharing for that port or protocol. As a rule, it is not possible to share the same port or the IP protocol ESP or GRE more than once in a network router like the FRITZ!Box.

Note:The FRITZ!Box checks all incoming and outgoing data packets and automatically rejects unwanted data from the Internet (Stateful Packet Inspection). The FRITZ!Box uses the NAT (Network Address Translation) mechanism to check incoming data and determine which port it is addressed to, which IP protocol it is transporting, and which device it should be forwarded to. If ports or IP protocols are shared more than once, it is no longer clear which device the data is intended for. Therefore, it is not possible to configure multiple port sharing rules with NAT.

1 Ports used by the FRITZ!Box

The FRITZ!Box itself uses some ports to provide functions such as Internet telephony. Here we give you an overview of ports that are typically opened by FRITZ!Box services:

Note:You can find a list of all the ports being used by your FRITZ!Box in the user interface under "Diagnostics > Security".

2 Using a different port

If Internet applications (for example chat software or online games) or several computers, game consoles or other devices connected to the FRITZ!Box require the same TCP or UDP port for incoming connections from the Internet, configure the devices or applications so that they all use different ports:

Important:IP protocols ESP and GRE can only be shared for one device. There is no workaround for these IP protocols.

Configure the device or application so that it does not use the same ports to accept connections from the Internet that are used by the FRITZ!Box, other devices, or other applications.

Important:If you use the same application on several computers, assign different ports for incoming connections in the application on each computer.